Markus Kainulainen (9 August 1922, Helsinki – 30 August 2017) was a Finnish communist politician.
He was a member of the Central Committee of the Communist Party of Finland (SKP) and served as a Member of the Parliament of Finland from 1975 to 1979 and again from 1982 to 1983, representing the Finnish People's Democratic League (SKDL).
After the SKP split in the 1980s, Kainulainen at first joined the Communist Party of Finland (Unity) (SKPy).
The SKPy split in 1988 as well and Kainulainen was one of the leading organisers of a new party, Communist Workers' Party – For Peace and Socialism (KTP).